I am downloading a file using Python urllib2. How do I check how large the file size is?

问题

And if it is large...then stop the download? I don't want to download files that are larger than 12MB.

request = urllib2.Request(ep_url)
request.add_header('User-Agent',random.choice(agents))
thefile = urllib2.urlopen(request).read()

回答1:

There's no need as bobince did and drop to httplib. You can do all that with urllib directly:

>>> import urllib2
>>> f = urllib2.urlopen("http://dalkescientific.com")
>>> f.headers.items()
[('content-length', '7535'), ('accept-ranges', 'bytes'), ('server', 'Apache/2.2.14'),
 ('last-modified', 'Sun, 09 Mar 2008 00:27:43 GMT'), ('connection', 'close'),
 ('etag', '"19fa87-1d6f-447f627da7dc0"'), ('date', 'Wed, 28 Oct 2009 19:59:10 GMT'),
 ('content-type', 'text/html')]
>>> f.headers["Content-Length"]
'7535'
>>>

If you use httplib then you may have to implement redirect handling, proxy support, and the other nice things that urllib2 does for you.

回答2:

You could say:

maxlength= 12*1024*1024
thefile= urllib2.urlopen(request).read(maxlength+1)
if len(thefile)==maxlength+1:
    raise ThrowToysOutOfPramException()

but then of course you've still read 12MB of unwanted data. If you want to minimise the risk of this happening you can check the HTTP Content-Length header, if present (it might not be). But to do that you need to drop down to httplib instead of the more general urllib.

u= urlparse.urlparse(ep_url)
cn= httplib.HTTPConnection(u.netloc)
cn.request('GET', u.path, headers= {'User-Agent': ua})
r= cn.getresponse()

try:
    l= int(r.getheader('Content-Length', '0'))
except ValueError:
    l= 0
if l>maxlength:
    raise IAmCrossException()

thefile= r.read(maxlength+1)
if len(thefile)==maxlength+1:
    raise IAmStillCrossException()

You can check the length before asking to get the file too, if you prefer. This is basically the same as above, except using the method 'HEAD' instead of 'GET'.

回答3:

you can check the content-length in a HEAD request first, but be warned, this header doesn't have to be set - see How do you send a HEAD HTTP request in Python 2?

回答4:

This will work if the Content-Length header is set

import urllib2          
req = urllib2.urlopen("http://example.com/file.zip")
total_size = int(req.info().getheader('Content-Length'))

来源：https://stackoverflow.com/questions/1636637/i-am-downloading-a-file-using-python-urllib2-how-do-i-check-how-large-the-file